This invention relates to an image forming apparatus such as a full color copying machine or color printer multi-function machine.
Generally, there are provided a plurality of methods for reading document data, particularly, in a scanner section of a document image processing apparatus which deals with image information.
For example, a method for reading document data while the document is being moved as in a facsimile machine (which is hereinafter referred to as a through read system), a method for reading document data while a carriage having the scanner section provided in the scanner is being moved without moving the document as in a flat bed scanner (which is hereinafter referred to as a document table fixed type system), a method for reading document data while the document table itself is being moved (which is hereinafter referred to as a document table moving type system), a method which is not generally used, for reading document data while the document is wound on a drum, and the like are provided.
Further, in the copying machine, there is provided a system in which documents are automatically drawn onto the document table one by one by an automatic document feeder (ADF) and the scanner section of a scanner is operated when the document is supplied on the document table. Thus, it becomes possible to copy a plurality of documents and input an image without much trouble.
However, since a document is drawn onto the document table and set still on the document table and then the document image is scanned and input when a plurality of documents are sequentially supplied by use of the automatic document feeder, it is necessary to temporarily fix the document on the document table. Therefore, it takes a lot of time to perform a series of processes and a bottleneck (difficulty) occurs when the operation speed is enhanced.
If the through read system is used as the document input system by use of the ADF in order to solve the above problem, it becomes unnecessary to keep the document still on the document table and it is possible to enhance the reading speed. At this time, the document placed on the document table can be scanned and read by the document table fixed type system without using the ADF.
However, if the document is scanned while it is being drawn at high speed by use of the through read system, the document will float or it may be warped or bent since it is moved so that the image density, color and sharpness will become different from those obtained by use of the document table fixed type system. That is, there occurs a problem that the same input information cannot be acquired if the document input system is changed.
As a measure to cope with the above problem, it is proposed that data is subjected to the reflectance ratio correction process immediately after the data is read by the scanning section of the scanner in a case where the document image is input in a monochrome signal form by use of the through read system. Simply by performing the above process, substantially the same signal as input data acquired when the document table fixed type system is used can be acquired without changing image process parameters used after the above process (Patent Application No. 2000-371889).
However, in a case where the document image is input in a color signal form by use of the through read system, there occurs a problem that RGB input values are simply individually changed and the resultant color will become different from the color which is originally desired even if color information items of three colors of R (red), G (green), B (blue) are subjected to the reflectance ratio correction process, for example. Thus, if the same process is performed as in the case wherein the document image is input in a monochrome signal form, the same output with the image density, color reproduction, sharpness and the like as that obtained in the case of the document table fixed type system cannot be attained.
That is, color signals of yellow (Y), magenta (M), cyan (C), black (B) used when data is printed will become different when the document supplied by the ADF is read by use of the through read system and when the document placed still on the document table is read.